This invention relates to improvements in or to windscreens which are made of synthetic resin and adapted for use with automotive vehicles such as motorcycles and motor tricycles.
A motorcycle in general is provided with a windscreen which are made of synthetic resin and which are arranged at a front portion of the vehicle body in the vicinity of the steering handle, for protecting the rider from the rain, the wind or other disturbances.
Conventionally, windscreens of this kind are mostly manufactured by means of a vacuum molding method, which typically comprises heating a sheet or flat blank of a thermoplastic synthetic resin such as polyethylene which has been obtained by means of calendering or extrusion molding, clamping the resulting softened synthetic resin sheet in a mold having a mold surface corresponding in shape to a desired article or windscreen, then producing a vacuum in a gap between the mold and the sheet to cause the sheet to be struck to the mold surface, and then cooling the sheet to room temperature to cause it to cure.
However, according to such conventional vacuum molding method, it is impossible to shape a synthetic resin windscreen with desired different thicknesses over its whole surface. For this reason, a conventional synthetic resin windscreen manufactured by the vacuum molding method has a screen surface main portion with the same thickness as a fitting edge portion. That is, the thickness of the screen surface main portion is larger than an actually required thickness, resulting in a large total weight of the synthetic resin windscreen.
Further, the screen surface main portion of a conventional synthetic resin windscreen has almost a whole surface extending straight from a location adjacent the fitting edge location to a portion adjacent the screen surface peripheral edge portion to present straight and flat side surfaces. Therefore, a windscreen of this kind has its wind shielding effect determined only by the height or whole longitudinal size of the screen surface main portion. Therefore, to obtain a larger wind shielding effect, the height of the screen surface main portion has to be increased. However, the synthetic resin windscreen with an enlarged screen surface main portion has a generally increased whole surface area, so that it undergoes increased air resistance during running of a motorcycle or a motor tricycle on which it is installed, and also has large whole weight.
Moreover, the synthetic resin windscreen manufactured by the aforementioned conventional vacuum molding method requires not only trimming of its screen surface peripheral edge portion after discharge from the mold, but also drilling to form holes and notches in the fitting edge portion at predetermined locations for fitting the windscreen to a vehicle body, since simultaneous formation of such holes and notches are impossible during the molding step according to the vacuum molding method. This requires a large number of man-hours for the manufacture of a windscreen, and also leads to a poor yield, resulting in high manufacturing costs.